The military wing of Hamas, a former ally of President Assad, is training the rebel Free Syrian Army in eastern Damascus. Diplomatic sources said that members of the Ezzedine al-Qassam Brigades were training FSA units in the rebel-held neighbourhoods of Yalda, Jaramana and Babbila.

The development appears to confirm that Hamas, the Palestinian militant group that runs the Gaza Strip, has made a final break with its former Syrian host and fully embraced the patronage of Qatar, the small but influential Gulf state that is a major financial and logistical backer of some rebel factions.

“The Qassam Brigades have been training units very close to Damascus. These are specialists. They are really good,” said a Western diplomat with high-level contacts in the Assad regime and the Syrian opposition who visits Damascus regularly.

Other sources suggested that Hamas trainers were helping the FSA to dig tunnels beneath at least one contested area of Damascus in preparation for a widely expected assault on the city centre. Hamas has extensive experience in tunnel-building in Gaza, to smuggle goods in from Egypt and to infiltrate Israel or launch attacks against Israeli targets.

Other sources suggested that Hamas trainers were helping the FSA to dig tunnels beneath at least one contested area of Damascus in preparation for a widely expected assault on the city centre. Hamas has extensive experience in tunnel-building in Gaza, to smuggle goods in from Egypt and to infiltrate Israel or launch attacks against Israeli targets.

A Palestinian source from Lebanon’s Ain al-Hilweh Palestinian refugee camp said that it was common knowledge that a few hundred Hamas militants were fighting alongside the FSA in the Yarmouk and Neirab Palestinian camps in Damascus and Aleppo, Syria’s commercial capital.

Any such link is vehemently denied by Hamas. Osama Hamdan, a leading Hamas official based in Lebanon, said: “It’s a false thing. There are no members of Ezzedine al-Qassam or any militant members of Hamas in Syria.

“We don’t interfere in the internal problems of Syria. Our members there are normal civilians, Syrian Palestinians, who live with their families there. From the beginning of what has happened in Syria we rejected as a movement any involvement of any Palestinian in the current events in Syria.”

The Assad regime gave shelter to Hamas in Damascus from 1999 when the group was expelled from Jordan. Hamas was a component of the “axis of resistance”, the pan-regional alliance that also grouped Iran, Syria, Lebanon’s militant Shia Hezbollah and smaller Palestinian factions.

However, when the uprising against the Assad regime erupted two years ago, Hamas found itself caught between its loyalty to the regime and obligations to its Palestinian supporters, who overwhelmingly sided with the Syrian opposition. Hamas, as the only significant Sunni member of the “axis of resistance”, risked angering the predominantly Sunni opposition in Syria by standing beside a regime that is drawn from the Alawite sect…

… Khaled Meshaal, Hamas’s top political leader, quietly slipped out of Damascus in February last year and moved to Qatar. That same month, Ismael Haniyah, the head of the Hamas Government in Gaza, openly declared the movement’s support for the Syrian opposition….

…. The state-run media accused Mr Meshaal of being “ungrateful and treacherous”.On Wednesday, following Mr Meshaal’s re-election as head of Hamas’ political wing for a fifth term, Ath-Thawra, a Syrian regime newspaper, said that he had shifted “the gun from the shoulder of resistance to the shoulder of compromise”.

Mr Meshaal “cannot believe his luck. After an acclaimed history of struggle, he has returned to the safe Qatari embrace, wealthy, fattened in the age of the Arab Spring’s storms,” it said.

There have been scattered reports of Hamas personnel travelling to Syria to participate in the rebellion. One Palestinian, identified as a Hamas trainer, was killed in Idlib in December. Hamas said that he had left the movement before travelling to Syria but nonetheless reportedly organised a lavish funeral for him.

Palestinian and Arab diplomatic sources said that if Hamas had dispatched military trainers to Damascus it was most likely at the behest of Qatar rather than a unilateral decision by the movement’s leadership.

Qatar is believed to be directing its support to military factions associated with the Muslim Brotherhood, the ideological parent organisation of Hamas. Qatar has also become the main paymaster for Hamas since the movement split from the Assad regime and funds from Iran have slowed.

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Hamas is thought to be using tunnelling expertise gained in GazaAFP/Getty

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Searching for casualties in an air strike on the al-Myassar neighbourhood of AleppoGiath Taha/Reuters